Explicitly-correlated coupled cluster method for long-range dispersion coefficients

Abstract

A method of calculation of long-range dispersion C6 coefficients with wavefunctions, corresponding to linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] model, has been developed. Designed approach uses CCSD(F12) wave functions for the calculation of dynamic polarizabilities at complex frequencies with further utilization of Casimir-Polder formula. As a part of the algorithm, the explicitly-correlated version of the coupled-perturbed CCSD equations for the case of complex frequencies has also been implemented. Numerical tests, conducted for the set of molecules show good agreement between dispersion coefficients, calculated with developed explicitly-correlated method and corresponding complete basis set results in regular CCSD already at triple-ζ level.